The state of Ti3+ ions formed at various steps of preparation and activation of highly active titanium-magnesium catalysts of various composition (dry milling of TiC13 with MgCl,; reduction of T i c 4 by nonsolvated magnesium dialkyl; interaction of the TiC14/MgCl s stem with an organoaluminium compound) was studied by the ESR method. It was found that In all systems studied the same three types of Ti3+ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCI,. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti3+ ions formed in all systems enter the composition of particles or surface aggregates of TiC13 and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium-magnesium catalysts are supposed to be constituents of these particles or of surface aggregates.
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The role of Ti3+ ions in titanium-magnesium catalysts of various composition, TiCb /MgCI, + AIR,, TiCb/MgC12 + Al(i-Bu), + EB, TiCb/EB/MgCI, + Al(i-Bu), and TiCb/EB/ MgCb + Al(i-Bu), + EB, was studied by means of ESR. The ESR data and the catalytic properties were compared. It could be shown that the introduction of ethyl benzoate (EB) leads to an increase of stereospecificity, to a considerable increase of the portion of Ti3 + ions which can be observed by ESR, to the appearance of several new signals in the ESR spectra and to an increase of the portion of titanium in solution, removed from the solid catalyst during the interaction with the organoaluminium cocatalyst. Titanium ions are found mainly in the particles or surface associates whose Ti3+ ions produce no signals in the ESR spectra, Ti3+ ions observed by ESR are found to be inactive centers of polymerization. The active centers appear to be localized in highly dispersed particles or surface associates of TiCI, , formed on the MgCI, surface and are not revealed in the ESR spectra. Increasing stereospecificity in the presence of EB is assumed to be caused by deactivation of non-stereospecific active centers with ethyl benzoate.
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